A new kid in our solar system? Hunt for mysterious ‘Planet Nine’ offers a surprise

PARIS: It’s an evocative idea that has long bedevilled scientists: a huge and mysterious planet is lurking in the darkness at the edge of our solar system, evading all our efforts to spot it.Some astronomers say the strange, clustered orbits of icy rocks beyond Neptune indicate that something big is out there, which they have dubbed Planet Nine. Now, a US-based trio hunting this elusive world has instead stumbled on what appears to be a new dwarf planet in the solar system’s outer reaches. And the existence of this new kid on the block could challenge the Planet Nine theory. Named 2017 OF201, the new object is roughly 700km across, according to a preprint study published online last week.That makes it three times smaller than Pluto. But that is still big enough to be considered a dwarf planet, lead study author Sihao Cheng of New Jersey’s Institute for Advanced Study said. The object is currently three times farther away from Earth than Neptune. And it’s extremely elongated orbit swings out over 1,600 times the distance between Earth and the Sun, taking it into the ring of icy rocks around the solar system called Oort cloud. It goes so far out, it could have passed by stars other than our Sun in the past, Cheng said.During its 25,000-year orbit, the object is only close enough to Earth to be observed around 0.5% of the time, which is roughly a century. “It’s already getting fainter and fainter,” Cheng said. The discovery suggests “there are many hundreds of similar things on similar orbits” in the Kuiper Belt beyond Neptune. After spending over half a year sorting through a difficult dataset in search of Planet Nine, Cheng said he was “lucky” to have found anything at all. Researchers are seeking time to point James Webb, Hubble and ALMA telescopes at their discovery. But Sam Deen, a 23-year-old amateur astronomer, has been able to track the dwarf planet candidate through old datasets. “OF201 is probably one of the most interesting discoveries in the outer solar system in last decade,” he said.Back in 1930, astronomers were searching for Planet X when they found Pluto, which became our solar system’s ninth planet. But Pluto was demoted to dwarf planet status in 2006. There are now four other dwarf planets, and Cheng believes 2017 OF201 could join their ranks. When researchers modelled its orbit, they found it did not follow the clustered trend of similar objects. This could pose a problem for Planet Nine theory, but Cheng said more data is needed. He hopes this huge planet is out there somewhere. “We’re in an era when big telescopes can see almost to the edge of universe,” he said. But what’s in our “backyard” largely remains unknown.